1. Field of the Invention
The present invention relates to a circuit breaker, and more particularly to a circuit breaker for detecting electrical overload to thereby interrupt a circuit providing power from a source to a load when overload occurs.
2. Description of the Related Technology
Generally a wiring circuit breaker and a current leakage circuit breaker are used in a house for prevention of electric shock accidents. The circuit breaker is used for protecting an electric line. In the case where the detected current of a circuit exceeds a reference current level while under a load, current passing through the inside of the circuit is higher than normal and heat is generated. This causes the bimetal element of the circuit breaker to bend and the circuit is interrupted. As a result, an electric source is not provided to a load of an electric device. In this case, because high current occurs instantaneously, heat is applied to the bimetal element so that the magnet of the circuit breaker is operated before the load of an electronic product is operated. Therefore, an electric source is not provided to an electric device. A current leakage circuit breaker functions not only as a circuit breaker but also for sensing an electric shock when a user may be shocked while using an electric device. Therefore, a user is prevented from receiving the electric shock.
A typical circuit breaker has a bimetal element for protecting an electric device from being overloaded. The bimetal is formed from two kinds of metal plates being attached by a rolling method, and the metal plates differ from each other in thermal expansion coefficient. Because the thermal expansion coefficients differ, the bimetal is bent in proportion to a change of temperature. Because this bimetal will bend significantly in proportion to a small change in temperature, it is widely used as a thermometer or a switch for detecting a change of temperature. The bimetal element equipped in a circuit breaker is capable of detecting overload and interrupting a circuit because it bends toward the metal with the low expansion coefficient when an over-current flows. The low expansion coefficient metal used in a bimetal includes an alloy of which the thermal expansion is very small. And, the high-expansion metal includes nickel-chrome-iron alloy, nickel-manganese-iron alloy or manganese-copper-nickel alloy, etc.
Because overload detection using a bimetal must keep detecting the over-current state during a predetermined period, for example, from four minutes to a hour, much time and expenditure is required to design overload detection and for testing the overload detecting circuit. Further, because the bending degree of a bimetal by over-current changes easily according to use over time, the operation characteristics of the overload-protecting circuit will change. Moreover, after the circuit is interrupted by the bending bimetal, the bent bimetal must be returned to its original state. However, much time is required for the bimetal to return to its original shape.
Recently, many circuit breakers have been manufactured as a combination type. The combination type indicates that a circuit breaker detects many kinds of electrical faults such as overload, arc fault and ground fault to thereby interrupt the circuit. Because high current passes through a conduction line when an arc fault occurs, the circuit breaker of this combination type sometimes mistakes the arc for overload. Because the arc fault occurs from a problem in a wiring line, a fire may occur when the circuit is reconnected unless the cause of the fault is identified. However, because overload is generated by a temporary over-current, reconnection of the circuit does not cause a problem after the circuit is interrupted. Therefore, the circuit breaker of the combination type should be able to detect the cause of circuit interruption. However, conventional circuit breakers are not able to precisely distinguish overload from arc fault.